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Fig. 8.4 Distribution of soils with a histic epipedon in the USA (Source: NRCS)
with a histic epipedon is about 161,000 km
2
or 1.7 % of the total area of the
country (Fig.
8.4
). The total area of Folists in the USA is 4,433 km
2
;
the Folists occur primarily in Alaska (41 %), Hawaii (38 %), and New England
(18 % of total).
8.5 Factors Influencing the Formation of Folistic
and Histic Epipedons
Folistic epipedons form in soils that receive abundant precipitation and feature high
biomass, as in temperate and tropical rainforests (Table
8.5
). They tend to occur on
steep slopes and on porous bedrock types. Soils with a histic epipedon form in areas
where precipitation exceeds evapotranspiration and commonly in areas receiving
more than 500 mm/yr of precipitation (Table
8.6
). Peatland vegetation types and
succession favor the development of soils with a histic epipedon. According to
Everett (
1983
), peatlands form at rates of 1-9 cm per 100 yr.
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